Lapping carrier



atented Get. 27, 1942 LAPPING CARRIER Franz R. Hensel, Earl I. Larsen, and Omar L. Fluharty, Indianapolis, Ind., assignors to P. R. Mallory & 00., Inc., Indianapolis, Ind, a corporation of Delaware No Drawing. Application September'lt), 1940, Serial No. 356,198

2 Claims.

- This invention relates to materials for lapping carriers used for producing extremely smooth and accurate surfaces.

It is an object of the present invention to provide lapping carriers which will produce a superior and very accurate finish.

It is another object of the invention to provide a lapping carrier with a predetermined and very uniform porosity, permitting a more effective charging of the lap.

Other objects of the invention will be apparent from the following description taken in connection with the following claims.

The present invention comprises the combination of elements, methods of manufacture and the product thereof, brought outand exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements, without departing from the spirit of the invention.

Up to the present time, lapping carriers are usually made of soft cast iron, copper, brass or lead. For most applications, where accurate work is desired, a soft, close grained cast iron is used. These lapping carriers are usually charged with abrasives such as emery flour, diamond dust, carborundum, alundum or other fine abrasives. The lubricants used are lard oil, machine oil, kerosene, gasoline, turpentine, alcohol, soda water. and the like.

There are usually two methods used for lapping; the wet method, where there is a surplus of oil and abrasive on the surface of the lapping carrier, and the dry method, where the lapping carrier is first charged and then all surplus oil and abrasive are washed oil. In the dry method, th lapping carrier surface is, however, also kept moistened with kerosene or gasoline.

To charge lapping carriers, a thin coating of. the prepared abrasive is usually spread over the surface and the surface and the lap is used in that manner until it ceases to cut.

The present invention contemplates a lapping carrier prepared from metal powders by pressing into suitable shapes, and slntering at a suitable pressure. The resulting metal composition is a lapping carrier, which lends itself much more readily to charging with the abrasives, since it contains uniformly distributed small cavities, 66

which act as receptacles for the abrasive media.

In order to obtain specific'properties of the lapping carrier, alloying ingredients may be added to the powders forming the matrix. In the case of iron, for instance, carbon, manganese, tungsten, molybdenum or similar ingredients may be added, which are commonly used in the manufacture of ordinary and special steels or cast irons. In the case of a copper base material, such ingredients as silicon, zinc, tin or aluminum may be added, which ingredients form the standard copper alloys, such as bronzes or brasses.

In addition to the soft metals mentioned above, it is contemplated that alloys composed of ,such soft metals may be used for the body or matrix of the lap. It is further contemplated to add such ingredients as lead, bismuth, calcium and the like, to such soft metal compositions, in order to improve their physical properties.

Below is given an example of a lapping material, made in accordance with the present invention.

Iron powder, having a particle size of -200 mesh, is pressed to a density of 4 to 5 grams per c. c. and sintered in a hydrogen atmosphere at a temperature of about 1000 deg. C. After this treatment, the pressed and sintered compact was quite strong and hard, even though it had to porosity. It has been found that by modifying the particle size of the powders, the sintering temperature and time, and the pressed density, the degree of porosity can be controlled within rather wide limits. For example: it an iron powder, having a particle size of 100 mesh is used, a porosity of 25% can be obtained; whereas, if an iron powder having a particle size finer than -325 mesh is used, a porosity of can be obtained.

Another means of controlling the porosity is by mixing various proportions of powders of different particle size. In the specific example mentioned above, the lapping carrier was prepared by pressing the powders cold, and sintering in a hydrogen, reducing or inert atmosphere,

at approximately 1000 deg. C.

A modification of this procedure, which hasheated to within a range at which welding occurs,

the application of pressure or impact of thepow ders, causes the various particles of powder to to lapping operations,

become welded or intimately bonded together,

resulting in a very strong metal body. The actual lapping test showed that using a pure iron produced a very suitable lap for very accurate work.

By molding and pressing the powders against a suitably shaped die surface little or no subsequent shaping or machining of the lapping carrier surface is necessary prior to use. The abrasive. oils or other lapping materials are simply applied to the pressed surface to prepare it for lapping operations.

While the present invention as to its objects and advantages has been described herein as car ried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to .cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

l. A lapping carrier of the type adapted to have its grinding surface charged with abrasive prior said carrier consisting of a porous body composed of metal powder sinterbonded together, some of the pores in said body extending through the grinding surface thereof.

2. A lapping carrier of the type adapted to have its grinding surface charged with abrasive prior to lapping operations, said carrier consisting of a porous body of iron powder sinter-bonded together, some of the pores in'said body extending through the grinding surfacethereof, said body having 25% to'50% of porosity.

FRANZ R. HENSEL. EARL I. LARSEN. 

